Extensible and swingable conveyance loader



Aug. 26, 1969 v A. s. SEIPOS 3,462,734

EXTENSIBLE AND SWINGABLE CONVEYANCE LOADER Filed Oct. 17, 1966 4 sh ets-sheet 1 INVENTOR mom-:w o. sswos BY SMrsM ATTORNEYS 4 SheetsSheet 2 A. G. SEIPOS I EXTENSIBIJE AND SWINGABLB CONVEYANCE LOADER 7 Aug. 26, 1969 Filed Oct. 17, 1966 FIGS Aug. 26, 1969 A. G. SEIPOS EXTENSIBLE AND SWINGABIJE CONVEYANCE LOADVER Filed Oct. 17, 1966 4 Sheets-Sheet :5

ANDREW G. SElPOS 225E625 W 523 u Aug. 26, 1969 A. (5. SEIPCS EXTENS1BLE AND SWINGABLE CONVEYANCE LOADER Filed Oct. 17, 1966 4 Sheets-Sheet 4 INVENTOR ANDREW G. SEIPOS ATTORNEYS United States Patent O 3,462,784 EXTENSIBLE AND SWINGABLE CONVEYANCE LOADER Andrew G. Seipos, Miami, Fla., assignor, by mesne assignments, to Wollard Aircraft Equipment Inc., Miami, Fla., a corporation of Washington Filed Oct. 17, 1966, Ser. No. 587,085 Int. Cl. B65g 11/00; 360k 17/30 U.S. CI. 14-71 9 Claims ABSTRACT OF THE DISCLOSURE An extensible and swingable conveyance loader pivoted at one end near a terminal building component and having an undercarriage supporting the extensible portion at a point spaced from the pivotal mounting, the undercarriage including ground engaging pivotally mounted wheels which have coordinated pivotal movement to support the extensible portion for inward and outward movement in one arrangement and to support the extensible portion for horizontal swinging movement in another arrangement, the undercarriage mobilizing structure permitting only longitudinal movement of the extensible portion in approaching the conveyance.

CROSS REFERENCE TO RELATED APPLICATION Andrew G. Seipos, Ser. No. 732,493, filed May 22, 1968.

BACKGROUND OF THE INVENTION It has already been proposed in extensible and swingable airplane loaders to provide mobile undercarriage for the outer ends of the loaders which will support the loader for in and out movement and also horizontal swinging movement as evidenced by U.S. Patents to Golde et al. 3,047,892, Der Yuen et al. 3,060,471, Lichti 3,123,167 and Moore et al. 3,184,772. As the length and weight of this type of loader have increased, known undercarriage construction has become inadequate and new ideas have become necessary in order to supply equipment which will be sufliciently rugged and still be economical to manufacture and maintain. When the number of wheels in the undercarriage is increased to sustain the heavier loads, complex mechanical problems are encountered in coordinating the wheels to achieve the swing movements and extension-retraction movements necessary to position the end of the loader at the airplane door. Additionally, in order to service the new, greatly enlarged airplanes, the height of these loaders has had to be considerably increased. This has resulted in lateral stability problems in respect to support of the outer end of the loader at the greater heights required. Finally, in practice, it has been learned that snaking a loader (illustrated in FIGURE 1 of 3,060,471) into servicing position relative to an airplane can result in damage to the airplane or the loader by other than substantially normal movement relative to the airplane. It has also been found that snaking results in lost time due to the high degree of skill required in this type of movement and the lack of experience in the personnel which customarily operate this type of equipment.

The prevent invention is a simple, rugged, economical structure which is stable and which can be operated in a simple manner by relatively inexperienced personnel.

DESCRIPTION OF THE INVENTION Reference is now made to the drawings in which: FIGURE 1 is a view in side elevation of one form of conveyance loader embodying the present invention;

FIGURE 2 is a fragmentary perspective view of the telescoping structure utilized in the loader of FIG- URE 1;

FIGURE 3 is a fragmentary view taken on the line 2-2 of FIGURE 1 with parts omitted for clarity;

FIGURE 4 is a plan view of the structure of FIG- URE 3;

FIGURE 5 is an elevational view in section taken on the line 5-5 of FIGURE 3 with parts broken away for clarity;

FIGURE 6 is a plan view in section taken on the line 66 of FIGURE 5;

FIGURE 7, is a schematic plan view showing various positions of the loader of the present invention in servicing airplanes; and

FIGURE 8 is a schematic flow diagram of hydraulic circuits applicable to control of the present invention.

In FIGURE 1, reference numeral 10 indicates generally an airport terminal building and 12 the usual concrete apron of the airplane loading area.

The loader of the present invention has the usual pivotal mounting structure indicated generally at 13 and disclosed more specifically in copending application Ser. No. 732,493. This pivotal mounting structure provides for both horizontal and vertical swinging movement but, insofar as the present invention is concerned, any conventional pivotal mounting structure providing for horizontal swinging movement will suffice and, since the details of this part of the loader form no part of the claimed invention, a specific description of all the parts of the pivotal mounting structure will not be given. An extensible, elongated passageway is indicated generally at 14 terminating in a conventional airplane vestibule, indicated generally at 16. The undercarriage structure embodying the major component of the present invention is indicated generally at 18; loader elevating structure is indicated generally at 20; and an outside stairway is indicated generally at 22. The airplane vestibule 16 and the outside stairs 22 form no part of the present invention and will not be further described.

Referring more particularly to pivotal mounting structure 13, a pedestal 24 supported on apron 12 in turn fixably supports a portion 26 of the building vestibule which includes a roof 27. On the upper end of pedestal 24, there is rotatably supported a member 28 which in turn supports the floor 29 of the terminal vestibule. Rotatable member 28 also supports a gimbal construction 30 which in turn supports a duplicate pair of arms 31 which form the end supporting elements of the first passageway section of the extensible, telescoping portion 14. Flexible curtains 32 enclose the sides of the terminal vestibule in known manner. It will thus be seen that extensible portion 14 of the loader is supported through the medium of arms 31 on rotatable member 28 thereby mounting this end of extensible portion 14 for horizontal swinging movement.

Extensible portion 14 of the loader can be any reasonable number of tunnel sections but is made up of telescoping sections 34, 35, 36, with the airplane end of tunnel section 36 being rigidly supported by elevating mechanism 20 and undercarriage 18. A casing 19 for the undercarriage is shown in FIGURE 1 but is omitted for clarity in some of the other figures.

The telescoping tunnel sections 34, 35, 36 can be supported within each other in any conventional manner, but in the present case utilize the construction diagrammatically illustrated as simply as possible in FIGURE 2 wherein the mating end portions of tunnel sections 34 and 35 are illustrated by way of example. Tunnel section 34 carries stops 38 at its four interior corners of its outer end and tunnel section 35 carries stops 37 at the four ice exterior corners of the end telescopically received by tunnel section 34. Positioned in between the exterior horizontal surfaces of tunnel section and the internal horizontal surfaces of tunnel section 34 along the sides thereof are roller bearing cages 39 which retain and position roller bearings in rolling contact with the opposed horizontal surfaces of tunnel sections 34 and 35. Thus as the telescoping portions of tunnels 34 and 35 move relative to one another, the weight of tunnel section 35 is carried on roller bearings 40 and roller bearing cages 39 move along with roller bearings 40, merely retaining the roller hearings in proper relative position to one another and to the surfaces of the tunnel sections. On outward movement of tunnel 35 the stops 37 and 38 determine the minimum overlap of the sections.

Supporting and elevating structure 20, disclosed more specifically in Ser. No. 732,493, incorporates a pair of vertical support members 42 which are telescopically received respectively within a pair of tubular guide members 43 rigidly mounted at the outer end of tunnel section 36. The lower ends of supporting members 42, as shown in FIGURE 3, are rigidly mounted on the undercarriage 18. A pair of extensible hydraulic motors 44 have their lower ends pivotally mounted on undercarriage 18, their upper ends suitably engaging and supporting the outer end of tunnel section 36 so that when extended and retracted the conveyance end of the loader will be raised and lowered relative to the ground on support members 42 running in guide members 43. The details of this elevating and lowering construction are not shown and described herein since insofar as the present invention is concerned only horizontal swinging movement of the loader is involved.

Referrring now specifically to the form of undercarriage 18 illustrated in FIGURES 3 to 6, inclusive, a structural frame members is shown at in the form of a built-up box girder on which are rigidly mounted support members 42 through the medium of attaching plates 51. This structural frame member carries hinge members 52 for pivotally supporting the lower end of extensible hydraulic motors 44. Outwardly spaced from the tunnel supporting means 51, 52 on structural frame member 50 are substantially identical vertical pivot mounting structures indicated generally by reference numerals 53 for a pair of substantially identical trucks indicated generally by reference numerals 54, one of these structures being best illustrated in FIGURE 5. Set into the box girder of structural frame member 50 is a vertically disposed bearing bushing 56 with its upper and lower ends welded to the plates of the box girder. Rotatably received within this bushing 56 is a vertical shaft 57 welded at its lower end to the upper member 58 of a horizontal pivotal structure indicated generally at 59. The lower member 60 of this horizontal pivotal structure includes a plate 61 resting on a still lower plate 62. The upper and lower members 60 and 68 of the horizontal pivotal structure 59 are interconnected by a horizontal shaft 64 received in openings in parts 58 and 60 and in a bearing bushing 65. Fixed and removable collars 66 and 67, respectively, maintain pin 64 in place. Returning to vertical shaft 57, a removable collar 68 retains the upper end. The lower end of shaft 57 has mounted thereon a bushing 70 which is welded thereto and in turn has welded to it a sprocket 71. Between the upper surface of sprocket 71 and the lower surface of structural frame member 50 is an orificed plate 72 of bearing metal surrounding the shaft 57.

Carried by the undersurface of plate 62 in each truck is a welded box-like structure 74 which rigidly supports a cylindrical shaft supporting tube 76 within which independently rotate shafts 77, 78 of wheels 79, 80. A sprocket 81 is rigidly connected through the drive bushing 82 to wheel and a chain drive 83 connects sprocket 82 with a pinion gear 84 driven by a hydraulic motor 85 supported on the lower surface of plate 62 by adjustable stud bolts 86.

The connections between plate 61 and plate 62 are such that these two plates can be moved relative to one another in the same plane for adjustment purposes around a pivot point 88 and within the limits of arcuate slots 89 and they can be locked in an adjusted position by stud bolts 90 which are threaded into plate 62.

As best illustrated in FIGURES 3 and 4, each of the two substantially identical trucks 54, although freely rotatable in a horizontal plane on shaft 57, are interconnected for identical angular movements by a mechanical means indicated generally by reference numeral 92. This means is made up of a continuous, taut, tension member having chain portions 93, 94 composed of links which consecutively engage the cogs on the associated sprockets and interconnecting tension members 96 which cross each other. By this means any swinging movement of one truck is transmitted in identical, reverse angularity to the other truck.

Bushing 70 has a lever arm 98 rigidly attached to it on each truck and each lever arm is in turn connected to the free end of a fluid actuated hydraulic cylinder or jack 99 which is pivotally mounted at 100 on a plate 101 carried by each end of structural frame member 50.

In respect to either one of the trucks adjustably positionable limit switch means (omitted in FIGURES 3 and 4 for simplicity) are arranged to act between lever arm 98 and structural frame member 50 as described in greater detail below.

It will be apparent from an inspection of FIGURES 4 and 6 that the adjustability between plates 61 and 62 is designed to facilitate coordination of hydraulic jacks 99, the horizontal swinging action of trucks 54 and the proper interconnection between chain links 94 and the cogs of sprockets 71. If plates 61 are aligned with the longitudinal axis of structural frame member 50 and the chains and sprockets interconnected (all as illustrated in FIGURE 4), by movement of stud bolts 90 in slots 89, the coaxial axes of the pair of wheels on each truck can be set at the exact angle desired relative to the longitudinal axis of the loader. As described in greater detail later, this angle is set so that the coaxial axes of the pair of wheels on each truck are on a radius passing through the vertical axis of the pivotal mounting carried by pedestal 24 on which the entire loader swings in a horizontal plane, when the loader is extended to a desired point intermediate its shortest length and its greatest length. Bolts 90 are then tightened to lock the trucks in this position. By setting plates 61 in alignment with the structural frame member 50, horizontal pivots 64 will be aligned when the trucks are in position for swing movement of the loader. This eliminates strain on the parts if the loader is elevated at this time and there is accommodating pivotal movement at pivot 64. When the loader is elevated with the trucks in extend-retract position accommodating pivotal movement can take place by rocking action on the four aligned wheels.

J'acks 99 when connected in operative relation in the hydraulic system will determine the angular position of the coaxial axes of the wheels of the trucks during rotative movement of the trucks on actuation of these jacks and coordinating means 92 will constrain the trucks to identical but opposite angular movement. Conveniently jacks 99 will be designed so that they are near their opposite extremities of movement when the plates 61 and 62 are locked in the adjusted position. Opposite movement of jacks 99 will cause the trucks to rotate in the horizontal plane, which action may or need not be assisted by the action of hydraulic motors 85, these motors in such case being driven in opposite directions during such operations, as described below. Jacks 99 are of the type in which fluid under pressure is admitted to both faces of the piston and closing the valves on the fluid in the two ends of the cylinder will anchor the trucks in a desired position.

Operation of the loader is illustrated in FIGURE 7. In Position I of FIGURE 7 the loader is shown in its fully retracted position with the trucks set for swinging movement in a horizontal plane. In this position the loader can be used as a nose-in loader in which an airplane, not shown, is positioned facing terminal building and the airplane vestibule is set in a lateral position, as shown, relative to the longuitudinal axis of the loader. When the airplane stops at a predetermined point, the loader swings around into servicing position with the airplane vestibule in registry with the door of the airplane.

When it is desired to service a large airplane such as that indicated in broken lines at 106 and with the loader in its fully retracted position, either parallel with the building to occupy as little ramp space as possible or in Position I, the loader is horizontally swung into Position II, in which the operator of the loader aims the loader at the door of the waiting airplane. Trucks 54 are then swung or rotated from the position shown in FIGURE 4 by extension of the right-hand jack 99 piston rod and retraction of the left-hand jack 99 piston rod until the coaxial axes of all four wheels are in a straight line parallel to the structural frame member and normal to the longitudinal axis of the extensible loader. Conveniently, the limit switch means (see FIGURE 8) areengaged by one the trucks in this position to deactuate the jacks thereby anchoring the trucks in this position. The loader then is extended by actuating motors 85 in the same direction and the loader passes through Position III into Position IV in registry with the door of the airplane. If the operator has miscalculated and the leader as it is extended toward the airplane assumes Position V, the loader is stopped and the trucks are actuated in a manner reverse to that just described to place the coaxial axes of the wheels of the trucks on, or Substantially on, radii passing through the center of rotation of the pivotal mounting at 13. The loader is then swung horizontally in the direction of the arrow until it is aligned with the door of the airplane. At this point, the operator in the airplane vestibule of the loader is relatively close to the airplane and when the trucks have been again moved into the longitudinal movement position, the loader is moved into engagement with the airplane. By virtue of the inherent operation of this loader an inexperienced operator is forced to approach the airplane solely by longuitudinal movement of the loader and not by a combined longitudinal and lateral movement which can easily damage the airplane and the loader.

If desired, the positions of the coaxial axes of the pairs of wheels of the undercarriage can be accurately located on the radii passing through the vertical axis of horizontal swinging movement of the loader at whatever distance the undercarriage is located away from this vertical axis. However, it has been found that with the longest loaders now contemplated, a position of the coaxial axes of the trucks corresponding to a position halfway between the two extreme positions of the loader, fully retracted and fully extended, performs satisfactorily for all practical purposes because the dilference in angularity between this intermediate position and the two extreme positions is not sufficient to cause excessive tire wear or strain on the parts.

The important elements of an hydraulic system for operating the undercarriage are diagrammatically shown in FIGURE 8, which includes representations of lever arms 98, jacks 99 and wheels 79, 79 and 80, 80. An hydraulic liquid reservoir is indicated at 110- with a pump 112 having its intake in communication with the reservoir and its outlet connected to a pressure line 114. A conventional pressure gauge 116 and relief valve 118 are connected to the pressure line with the relief valve outlet communicating With the reservoir 110. Pressure line 114 branches to supply pressure fluid through branch line 120 to means for operating the jacks 99. After passing through an adjustable flow valve 122 for limiting the maximum flow rate, the hydraulic pressure fluid enters a tandem spool, solenoid operated, hydraulic valve 124 which is illustrated by the accepted symbol of the Joint Industrial Congress. At each end of valve 124, operating solenoids 126, 128 are arranged to move the spool valve into any one of the three positions diagrammatically illustrated in boxes 130, 132 and 134. Utility lines 136, 138 from the spool valve are connected to opposite ends of the cylinders of jacks 99 with line 136 being connected to the piston head end of the cylinder of the right-hand jack and to the piston rod end of the cylinder of the lefthand jack. In like manner, line 128 is connected to the other ends of the cylinders of jacks 99. With both solenoids 126, 128 deenergized, the spool valve assumes the position in which the pressure line bypasses the valve to exhaust fluid into exhaust line 123 which returns the fluid to sump from which the fluid is returned in any desired manner to reservoir 110. In this position of the spool valve, utility lines 136 and 138 are closed as illustrated by the box 130. When push button switch 140 is actuated and solenoid 126 is energized, the spool moves to the right and pressure line 120 is connected as shown by box 132 so that utility line 138 becomes the pressure line and utility line 136 becomes the exhaust line. When push button switch 142 is actuated and solenoid 128 is energized, pressure line 120 and exhaust line 123 are connected to utility lines 136, 138, respectively, as indicated by box 134, so that utility line 136 becomes the pressuer line and utility line 138 becomes the exhaust line. If both solenoids are energized or deenergized at the same time the valve assumes the intermediate position in which the pressure fluid bypasses the valve and utility lines 136 and 138 are blocked. One side of a power source 144 is connected through the closed side 145 of a pair of coupled switches 145, 146 to the parallel solenoid circuits with the other side of the power source being connected with ground. A pair of limit switches 148, are connected in the other side of each solenoid circuit to ground. As diagrammatically illustrated, movement of the left lever arm 98 into either one of two extreme positions actuates the associated limit switch.

Now referring to FIGURE 4, it will be seen that actuation of push button switch 142 with resultant energization of solenoid 128 causes the high pressure hydraulic fluid to be connected to the piston head end of the cylinder of the right-hand hydraulic jack 99 and to the piston rod end of the cylinder of the left-hand hydraulic jack 99. This causes the trucks to rotate, the right one counter-clockwise and the left one clockwise. As described above, the indicated lever arm 98 will eventually engage the actuating member of limit switch 148 thereby opening the electrical circuit to solenoid 128. The spool valve 124 will then move into the intermediate position where utility lines 136 and 138 are blocked thereby anchoring the trucks in that extreme position in which the axes of all the wheels are substantially aligned along a straight .line normal to the longitudinal axis of the loader. This also relieves the back pressure on pump 112 since the pressure fluid is exhausted into line 123 and sump 125. Actuation of push button switch 140 will energize solenoid 126 and the reverse operation will take place until the lever arm 98 actuates limit switch 150 at a predetermined point. This point is the one where the axes of the wheels of each truck are either radially disposed relative to the point at which the loader is pivotally mounted for horizontal swinging movement or are disposed in proximate relationship to this radial line, as described above. In the latter case the axes can be said to be disposed substantially radially relative to the point at which the loader is pivotally mounted for horizontal swinging movement.

Returning to FIGURE 8, second and third pressure lines 152, 154 are connected to tandem spool solenoid operated hydraulic valves 153, 155, similar to those just described, which control the application of the pressure fluid to the hydraulic motors driving wheels 80, as diagrammatically illustrated. In these cases, the fluid motors are prevented from operating with the spools in the intermediate position and their rotation directed in opposite directions by the two extreme positions of the spools. Electrical circuits similar to those described above are utilized in connection with the solenoids of each valve.

Control push button switches 157 and 158, respectively, direct electrical power to the solenoids 160, 162 and 164, 166 of valves 153 and 155. As mentioned previously, switches 145 and 146 are coupled so that only one of them can be closed at a time. This isolation of the hydraulic jack operation circuit and the wheel motor circuit can be accomplished in any desirable manner but for simplicity is shown in the form of mechanical coupling 168 which pivots on a fixed fulcrum 169 to close one switch while opening the other.

Reference to FIGURE 4 will show that both wheels 80 will be driven in one and the same direction in order to extend the loader and in the reverse direction to retract the loader. This is also the case when swinging the loader to the left or right. Thus, solenoids 160, 162 on the two spool valves 153, 155 will be energized at the same time and the solenoids 164, 166 of the two spool valves 153, 155 will be energized at the same time to bring about the desired movements of the loader.

Since in the intermediate positions of the spool valves 153, 155 the wheel motors are blocked against movement and wheels 80 can not be rotated, provision must be made to rotate wheels 80 in correct and opposite directions thereby assisting jacks 98 in rotating the trucks. This is accomplished by connecting solenoids 160 and 166 in parallel with solenoid 128 and solenoids 162 and 164 in parallel with solenoid 126. Then with a switch 170 and a switch 172 in each of these parallel lines and a switch 174 and a switch 176 for opening the circuits between solenoids 160 and 162 and between solenoids 164 and 166, respectively, all coupled to switch 145 in a mannor that causes switches 170 and 172 to close and switches 174 and 176 to open when switch 145 is closed and vice versa when switch 145 is open, the motors of wheels 80 will be driven in the proper direction to assist jacks 98 in rotating the trucks 154. As with jacks 99, actuation of limit switches 148 and 150 stops the wheel motors when the trucks have been rotated the desired degree.

I claim:

1. A conveyance loader comprising (a) an elongated, extensible passageway means pivotally mounted adjacent a terminal building for horizontal swinging movement,

(b) a mobile undercarriage supporting the extensible pasageway means at a point spaced from the pivotal mounting, the mobile undercarriage including:

(c) structural frame means connected in supporting relationship with the extensible passageway means,

(d) first wheel mounting means,

(e) second wheel mounting means,

(f) a first ground engaging wheel means, having an axis of rotation, carried by the first wheel mounting means,

(g) a second ground engaging wheel means, having an axis of rotation, carried by the second wheel mounting means,

(h) first pivot means associated with the first wheel mounting means placing the first wheel means in supporting relationship to the structural frame means, the first pivot means positioning the first wheel mounting means for rotating movement around an axis substantially normal to the ground,

(i) second pivot means associated with the second wheel mounting means placing the second wheel means in supporting relationship to the structural frame means, the second pivot means positioning the second wheel mounting means for rotating movement around an axis substantially normal to the ground,

(j) means for rotating the first wheel mounting means about the first pivot means,

(k) power means for acuating means (j),

(1) means for rotating the second wheel mounting means about the second pivot means,

(m) means interconnecting means (j) and means (1) for causing simultaneous rotational movement of each wheel mounting means through a predetermined angular movement between two extreme positions,

(n) means for stopping the simultaneous rotational movement of each wheel mounting means in one extreme position of the wheel mounting means when the axes of rotation of the first and second wheel means extend transversely of the longitudinal dimension of the passageway means and in the same direction,

(0) means for stopping the simultaneous rotational movement of each wheel mounting means in the other extreme position of the wheel mounting means when the axis of rotation of the first and second wheel means are substantially radially disposed relative to the pivotal mounting of the extensible passageway,

(p) means associated with each wheel mounting means for restraining each wheel mounting means against pivotal movement around the first and second pivot means when the wheel mounting means are in the one extreme position, and

(q) means associated with each wheel mounting means for restraining each wheel mounting means against pivotal movement around the first and second pivot means when the wheel mounting means are in the other extreme position.

2. Apparatus as claimed in claim 1 in which means (m) act between means (j) and means (I) to constrain the rotational movement of each wheel mounting means to substantially identical but opposite angular movement.

3. Apparatus as claimed in claim 2 in which (r) means (j) comprise sprocket means associated with the first wheel mounting means,

(s) means (I) comprise sprocket means associated with the second wheel mounting means, and

(t) means (In) comprise chain means coacting with each sprocket means and tension members connecting and maintaining the chain means taut.

4. Apparatus as claimed in claim 2 in which the coordinating means comprise (11) means carried by the first wheel mounting means projecting laterally from the first pivot means in a direction transverse to a line extending between the first and second pivot means when the wheel meansare in the one position,

(0) means carried by the second wheel mounting means projecting laterally from the second pivot means in a direction transverse to a line extending between the first and second pivot means when the wheel means are in the one position,

(-p) means connecting means (n) on one side of the line with means (0) on the other side of said line, the length of means (p) and the points of connection of means (p) with the associated wheel mounting means being such that on movement of the first wheel mounting means from the one position to the other position, tension on means (p) constrains the second wheel mounting means to move to the other position.

5. Apparatus as claimed in claim 1 comprising:

(1) power means associated with a wheel of each wheel means for driving such wheel so as to rotate such wheel in either direction, and

(m) means preventing rotation of the driven wheel of the first and second Wheel means in the same direction during movement of the wheel mounting means between the two extreme positions.

6. Apparatus as claimed in claim 1 in which each wheel means comprises a pair of wheels, the wheel mounting means mounting each wheel for independent rotation about axes of rotation which are coaxial with one another.

7. Apparatus as claimed in claim 1 in which (r) second power means are connected to a wheel of each wheel means for driving both wheel means to extend and retract the loader, and

(5) power means (k) act between at least the first wheel mounting means and the structural frame means for causing rotational movement of the wheel mounting means.

8. Apparatus as claimed in claim 7 in which control means are associated with power means (k) and the second power means which act to block operation of one power means while the other power means is operating.

9. In a conveyance loader having elongated passageway meanst pivotally mounted adjacent a terminal building for horizontal and vertical swinging movement and a mobile undercarriage supporting the extensible passageway means at a point spaced from the pivotal mounting for the horizontal and vertical swinging movement of the passageway means, the mobile undercarriage comprising (a) structural frame means connected in supporting relationship with the passageway means,

(b) first wheel mounting means and second wheel mounting means,

(c) a first ground engaging wheel means, including a plurality of wheels mounted for coaxial rotation, carried by the first wheel mounting means,

(d) a second ground engaging wheel means, including a plurality of wheels mounted for coaxial rotation, carried by the second wheel mounting means,

(e) first pivot means laterally disposed relative to the longitudinal axis of passageway means associated with the first wheel mounting means placing the first wheel means in supporting relationship to the structural frame means, the first pivot means positioning the first wheel mounting means for pivotal movement around an axis substantially normal to the ground,

(f) second pivot means associated with the second wheel mounting means placing the second wheel means in supporting relationship to the structural frame means, the second pivot means positioning the second wheel mounting means for pivotal movement around an axis substantially normal to the ground,

(g) third pivot means associated with the first wheel mounting means acting in conjunction with the first pivot means to place the first wheel means in supporting relation to the structural frame means, the third pivot means positioning the first wheel mounting means for pivotal movement around an axis parallel to the ground,

(h) fourth pivot means associated with the second wheel mounting means acting in conjunction with the second pivot means to place the second wheel means in supporting relation to the structural frame means, the fourth pivot means positioning the second wheel mounting means for pivotal movement around an aXis parallel to the ground,

(i) means associated with the first wheel mounting means and the second wheel mounting means for restraining each wheel mounting means against pivotal movement around the first and second pivot means when the axes of rotation of the first and second wheel means are substantially radially disposed relative to the pivotal mounting of the passageway means,

(j) means associated with each wheel mounting means rigidily positioning the axes of the third and fourth pivot means in coaxial relation to each other when the axes of rotation of the first and second wheel means are substantially radially disposed relative to the pivotal mounting of the passageway means, and

(k) means associated with the first wheel mounting means and the second wheel mounting means for restraining the first and second wheel mounting means against pivotal movement around the first and second pivot means when the weel mounting means are in positions in which all the wheels of the ground engaging wheel means make engagement with the ground at points disposed along a straight line normal to the longitudial axis of the passageway means whereby the undercarriage can pivot in a vertical plane on the wheel means to accommodate vertical swinging movement of the passageway means.

References Cited UNITED STATES PATENTS 1,162,640 11/1915 Morton -50 1,612,393 12/ 1926 Mossay.

1,901,276 3/1933 Adams.

2,598,863 6/1952 Tucker 180-50 2,863,518 12/ 1958 Pellizzetti.

2,688,761 9/1954 Good et al. 1471 3,123,167 3/1964 Lichti 14-72 XR 3,184,772 5/1965 Moore et al. 14-71 3,315,291 4/1967 Wollard et al. 1471 OTHER REFERENCES Passenger Speedway by Wollard Aircraft, pp. 11 and 12 (14-71) received Feb. 6, 1966.

JACOB L. NACKENOFF, Primary Examiner US. Cl. X.R. 180-45, 50 

